Application Solution‌

Executive Summary

Retrofitting automation for legacy wastewater treatment plants presents two major pain points: high civil‑engineering costs for new cable trenching, and the risk of modifying already‑stable PLC program logic. This real‑world case demonstrates how to leverage existing on‑site industrial WiFi access‑points to build transparent wireless Layer‑2 communication between PLCs and SCADA HMI systems. No changes are required to the original automation setup, cutting construction costs while complying with on‑site IT network security policies.

Retrofitting automation controls at older wastewater facilities often creates a dilemma. Plant buildings and processing tanks are widely dispersed with extensive steel structures. Running new network cabling requires trenching civil works, which drives up project costs, extends construction timelines, and may disrupt ongoing plant operations.

More critically for plant owners and system integrators: existing PLC and SCADA systems have run stably for years. Any edits to PLC logic or HMI configuration carry unpredictable production‑halt risks.

Is there a practical approach that avoids large‑scale civil cabling work and leaves legacy automation workflows completely untouched?

This article shares a real‑world retrofit project for a wastewater treatment facility. Using WideIOT WR713 industrial wireless routers and re‑using pre‑installed industrial WiFi‑AP infrastructure, a transparent Layer‑2 wireless local‑area network was deployed. It fully replaces the original wired links and enables stable mutual communication among multiple PLC units and SCADA operator workstations.

Customer Requirements

The plant’s legacy automation system operated over wired Ethernet, consisting of:

• 1 × Schneider M430 Master PLC
• 4 × Siemens S7‑200 Slave PLCs
• 1 × SCADA monitoring workstation

As plant upgrades proceeded, the original wired network infrastructure could no longer satisfy operational demands. Running new physical cabling would be technically difficult and capital‑intensive. The customer defined three non‑negotiable requirements:

1. Achieve full bidirectional communication between master PLC, slave PLCs and SCADA workstation with reliable Modbus‑TCP polling and read‑write operations.
2. Make zero modifications to existing PLC programs and SCADA configuration parameters to eliminate production risks introduced by program alterations.
3. Tolerate high‑humidity and heavy electromagnetic‑interference conditions typical of wastewater sites; integrate wireless devices under the plant’s central IT management policy, support internal‑network security controls and automatic fault self‑recovery.

Solution Design

No additional wireless base‑stations were deployed. Existing on‑site industrial WiFi‑AP hardware was reused. A flat network architecture was adopted: one WR713 industrial wireless router assigned to each automation device, connecting locally to the plant WiFi.

All six WR713 units operate in STA station mode to join the on‑site WiFi, forming a transparent Layer‑2 industrial LAN.

Key design merits:

1. All data stays within the private local network; no public‑internet traversal, no cellular data charges, eliminating external cybersecurity exposure.
2. Flat topology: the failure of one single router only impacts its attached device, it cannot cause total‑plant automation outage.
3. IP addressing, WiFi SSID and encryption schemes strictly follow the customer’s existing IT specifications. WideIOT devices perform only access‑side adaptation without building isolated private networks, making it easier to pass the owner’s network‑security review.

Why Choose the WR713 Industrial Wireless Router?

The WR713 is a high‑performance dual‑band WiFi industrial‑grade router engineered for harsh industrial environments, well‑suited for demanding water‑treatment operating conditions.

• Supports 2.4 GHz / 5.8 GHz dual‑band WiFi. STA‑mode transparent Layer‑2 forwarding provides native Modbus‑TCP pass‑through. No protocol conversion required, enabling zero‑change operation for existing PLC and SCADA software.
• Gigabit Ethernet ports with 1.5 kV electrical isolation, providing immunity against strong electromagnetic interference generated by water pumps and variable‑frequency drives.
• Wide industrial operating temperature: ‑20 °C ~ 70 °C; metal IP30‑rated enclosure, resistant to high humidity and dust inside wastewater facilities.
• Hardware watchdog timer, link‑quality monitoring and automatic reconnection for unattended plant operation with autonomous fault recovery.
• Static‑IP configuration capability plus built‑in firewall, seamlessly integrating into the plant’s existing network topology and safeguarding private‑LAN cybersecurity.

Project Acceptance & Validation

Full stability testing was completed after commissioning against clear, measurable acceptance criteria:

• Continuous ping tests across all network‑connected devices showed zero packet loss; the SCADA workstation successfully read and wrote data to every master and slave PLC.
• Cyclical Modbus‑TCP polling from the Schneider master PLC to the four S7‑200 slave PLCs ran consistently, with accurate data acquisition and command delivery.
• Simulated wireless‑link outages triggered fast automatic re‑establishment of communications.
• A 72‑hour continuous burn‑in test was completed without disconnections or data anomalies.

Solution Benefits

By deploying industrial routers to create transparent Layer‑2 wireless links, this wastewater‑plant project overcomes common challenges: geographically scattered equipment, difficult cable‑routing construction, and high risks associated with shutdown‑required retrofits. Balancing reliability and cost‑effectiveness, wireless infrastructure acts as an alternative to conventional wired cabling and delivers a lightweight implementation blueprint for inter‑site connectivity across water‑utility facilities.

1. Zero changes to operational business logic, avoids downtime risks Existing PLC firmware and SCADA configurations remain untouched, eliminating production‑outage hazards caused by retrofit debugging.
2. Re‑use existing WiFi infrastructure, shorten project timelines Leverages pre‑deployed plant WiFi access‑points, removing civil‑works trenching‑and‑cabling costs and compressing overall construction schedules.
3. On‑premises‑only data transmission, security‑compliant All traffic stays inside the private local‑area network with no public‑internet transit. Aligns with corporate IT governance and internal cybersecurity requirements.
4. Self‑healing links reduce maintenance overhead Fault‑isolation topology combined with industrial‑grade auto‑recovery mechanisms fits unattended wastewater‑plant operating profiles.
5. Turn‑key project delivery with complete documentation End‑to‑end services covering site survey, configuration, deployment and acceptance. Full‑set engineering documentation is provided to reduce integration partners’ implementation workload.

If you are facing cabling constraints and require wireless LAN connectivity between PLCs and host SCADA systems at your plant, reach out for solution documentation and technical discussions.